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The recent (apparent) passage of the Voyager 1 spacecraft into interstellar space provides us with front-row seats to the complex interplay between the solar wind and the protective surrounding bubble known as heliosphere. The heliosphere extends radially out to $sim100$ AU from the sun, and within this sphere of influence, the solar wind modulates the incoming flux of galactic cosmic rays (CRs), especially those at low energies. Newly formed stars, which support both strong magnetic fields and winds, are expected to produce analogous regions of CR exclusion, perhaps at elevated levels. Such young stars are encircled by molecular gas-rich disks, and the net removal of CRs from the circumstellar environment significantly reduces the expected CR ionization rate in the disk gas, most likely by many orders-of-magnitude. The loss of ionization reduces disk turbulence, and thereby affects both planet-formation and active chemical processes in the disk. We present models of CR exclusion and explore the implications for turbulence and for predicted chemical abundances. We also discuss means by which ALMA can be used to search for extrasolar heliosphere-analogs around young stars.
We assess the ionising effect of low energy protostellar cosmic rays in protoplanetary disks around a young solar mass star for a wide range of disk parameters. We assume a source of low energy cosmic rays located close to the young star which travel
To understand how the circumstellar environments of post-AGB stars develop into planetary nebulae, we initiate a systematic study of 2D axisymmetric hydrodynamic simulations of protoplanetary nebula (pPN) with a modified ZEUS code. The aim of this fi
Global evolution and dispersal of protoplanetary disks (PPDs) is governed by disk angular momentum transport and mass-loss processes. Recent numerical studies suggest that angular momentum transport in the inner region of PPDs is largely driven by ma
We give a review of cosmic ray propagation models. It is shown that the development of the theory of cosmic ray origin leads inevitably to the conclusion that cosmic ray propagation in the Galaxy is determined by effective particle scattering, which
It has recently been shown that the inner region of protoplanetary disks (PPDs) is governed by wind-driven accretion, and the resulting accretion flow showing complex vertical profiles. Such complex flow structures are further enhanced due to the Hal